This project focuses on the regulation and function of the MAPK Kinase Kinase MEKK3. MAPK pathways have been shown as essential to cell growth, differentiation and apoptosis. It is therefore of interest to gain a better molecular understanding of i) all of the component parts that make up these signaling paths, and ii) of the physiologic targets of individual MAPK pathways in normal and diseased states. We originally cloned MEKK3 and determined that it can activate all four major MAPKs, namely ERK, JNK, p38 and ERK5, albeit to different extents. We also discovered that MEKK3 arrests growth, protects from some apoptotic insults and activates NF-kappaB. Recently, MEKK3 was proposed to have a direct role in activating the IKK kinase complex, a critical complex that phosphorylates and thus causes degradation of the inhibitors of NF-kappaB. We have now cloned an adapter protein that directly links MEKK3 with the IKK kinase complex. This expanded complex may also contain AKT, since we have discovered an interaction between AKT and MEKK3. The AKT kinase has been implicated in many survival (anti-apoptotic) pathways, as has NF-kappaB. Therefore, these data link the AKT kinase to both MAPK pathways and to IKK/NF-kappaB via MEKK3 and a specific adapter, constituting a much larger complex that may be critical to cell survival. Other IKK-associated complexes may exist in addition, such as one containing the CIKS adapter protein,recently cloned in our laboratory.